Carpets made from polymer yarns, and particularly polyamide yarns such as nylon, are popular floor coverings for residential and commercial applications. Such carpets are relatively inexpensive and have a desirable combination of qualities, such as durability, aesthetics, comfort, safety, warmth, and quietness. Further, such carpets are available in a wide variety of colors, patterns, and textures. Polymer, and particularly polyamide, yarns are preferred for carpeting because they can be dyed easily with acid or other types of dyes. While dyeing is the most common method to obtain various carpet colors, color fastness is an issue. Ultraviolet light degrades the appearance of dyed carpet. Pre-metallized dyes can provide dyed articles and carpets having better light fastness, but these dyes are expensive. Additionally, their large molecular structure tends to make them more sensitive to small differences in the yarn, so they tend to dye somewhat less evenly than standard small molecule “work-horse” acid dyes. Pre-metallized dyes are also somewhat less environmentally acceptable than non-metallic dyes, so they can present waste disposal problems.
Colored pigments have long been incorporated into the fibers comprising polyamide and other polymer yarns to create durable colored carpets which maintain their color in spite of wear because, unlike most dyed fibers, the color is incorporated throughout the fiber.
For example, as described in U.S. Pat. Nos. 5,108,684 and 5,830,572, both to Anton et. al. (“Anton”), the specifications of which are hereby incorporated by reference in a manner consistent with this disclosure, the white pigment TiO2 is added in small quantities to nylon yarn as a delustering agent for nylon. Additionally, colored pigments may be added to the molten copolymer prior to spinning and drawing to improve the resistance of the yarn to degrading and fading in ultraviolet light. In Anton, color pigment concentrations added to the molten copolymer ranged from about 5900 ppm to about 8100 ppm. Anton discloses how most colored pigments cause difficulties during mixing into the copolymer and also during spinning and drawing operations. In Anton, materials which confer cationic dyeability on the polymer, such as aromatic sulfonates or their alkali metal salts, are also incorporated into the yarn prior to spinning to render the polymer resistant to acid dyes. Yarns made according to the invention of Anton are suitable as stain-resistant, pigmented nylon resins.
U.S. Pat. No. 5,562,871 to Hoyt et. al. (“Hoyt”), the disclosure of which is hereby incorporated by reference in a manner consistent with this disclosure, discloses incorporating color pigments along with SO3H groups or salts thereof that resist anionic dyes. Fibers made according to the invention of Hoyt provide stain resistant polyamide fibers. Hoyt discloses examples containing about 500 ppm carbon black to provide a lightly pigmented grey color to the yarn.
U.S. Pat. No. 5,445,653 to Hixson et. al. (“Hixson”), the disclosure of which is hereby incorporated by reference in a manner consistent with this disclosure, discloses a method of dyeing nylon, particularly cationic dyeable Type 6 and 66 nylon and light dyeable Type 66 nylon so that the dyed fiber will resist taking on further dye. Yarns made according to the invention of Hixson have a high degree of wash and bleed fastness. Hixson notes that yarns made by incorporating color pigment into the yarn results in the availability of only a few solid colors, limiting design creation.
U.S. Pat. No. 5,066,308 to Yeh et., al. (“Yeh”), the disclosure of which is hereby incorporated by reference in a manner consistent with this disclosure, discloses the addition of color pigment to yarns for preparation of patterned textile fabrics such as carpeting. Sufficient pigment is incorporated into the nylon prior to extrusion during the fiber melt spinning process such that the pigmented yarn can be detected visually to provide a good identifier to distinguish it from other yarns during the manufacturing process of the patterned fabrics.
Such color pigmented fibers enjoy permanent coloration which is not removed by washing, and are more resistant to degrading and fading under ultraviolet light and exhibit improved resistance to chemicals and nitrous oxide fumes than dyed fibers. However, the process of adding pigments to fibers tends to be more expensive than dyeing, especially at the high pigment concentrations required for deep colors. While pigmented fiber offers color fastness advantages, the number of colors required to satisfy customer preferences in the market place is huge and the cost of manufacture and inventory maintenance increases dramatically as the number of available colors increases. Therefore, pigmented fibers of the prior art are not well suited for use in efficiently producing a wide variety of substantially uniform color carpets.
One objective of the invention therefore is to provide a carpet or other overdyed article which enjoys the superior durability of pigmented polymer fiber, such as polyamide (e.g., nylon) fiber, along with the quality of appearance, color, dye depth, and ease of manufacture that dyeing processes yield today.
Another objective of the invention is to develop a new method whereby substantially uniform color polymer-based yarns and articles, such as polyamide (e.g., nylon) carpets, can be overdyed easily with “work-horse” acid dyes, but at the same time provide improved color and dye light fastness properties similar to that provided in articles manufactured with pigmented fibers.